Field of the Invention
The present invention relates to a photoelectric conversion device and an imaging system.
Description of the Related Art
As a photoelectric conversion device which is used for an image sensor of a camera or the like, a stacked-type photoelectric conversion device has been proposed. In a photoelectric conversion device disclosed in FIG. 1 of International Publication No. WO 2012/004923, a photoelectric conversion film is stacked over a semiconductor substrate. A transparent electrode is arranged on the photoelectric conversion film and a pixel electrode is arranged under the photoelectric conversion film. An insulating film is arranged between the photoelectric conversion film and the pixel electrode. The International Publication No. WO 2012/004923 discloses such a point that since correlated double sampling (hereinbelow, referred to as CDS) can be performed by such a configuration, noise can be reduced.
In the photoelectric conversion device disclosed in the International Publication No. WO 2012/004923, a reset of an electric potential of a pixel electrode is performed just before a signal readout. The reset of the electric potential of the pixel electrode is performed to set the electric potential of the pixel electrode to a specified value. However, since the electric potential of the pixel electrode is not fixed during an accumulation period and is a floating state, as a light signal is accumulated into an interface between a photoelectric conversion film and an insulating film during the accumulation period, a curve of an energy band of the photoelectric conversion film approaches a flat band state. At this time, the electric potential of the pixel electrode in the floating state changes by an influence of a change in electric potential of the photoelectric conversion film. Since a difference between the electric potential of the pixel electrode and the curve of the energy band when the light signal is accumulated in the interface between the photoelectric conversion film and the insulating film becomes a dynamic range of the light signal which can be detected, the foregoing change in electric potential of the pixel electrode occurs in a decreasing direction of the dynamic range of the detectable light signal.